Control apparatus for sheet feeding devices



D. BROIDQ Sept. 12,1944.

CONTROL APPARATUS FOR SHEET FEEDING DEVICES Filed May 18, 1942 5 Sheets-Sheet l n m M N .lllmrr llll A.

IUUDIDUDUIWV HIDUUIIUIDII U U IU U UUID D. BROIDO Sept. 12, 1944.

CONTROL APPARATUS EOR SHEET FEEDING DEVICES Filed May 18, 1942 5 Sheets-Sheet 2 I A77O/P/VEV Sept. 12, 1944. D. ammo 2,

- CONTROL APPARATUS FOR SHEET FEEDINQDEVICES Filed May 18, 1942 5 Sheets-Sheet 4 NVVE/VTOR A TTORIV Y l 1944- p. BROIDO 2,358,051

common APPARATUS FOR smear manna; pavrcas Filed May 18, 12542 5 Sheets-Sheet 5 Patented Sept. 12, 1944 CONTROL APPARATUS FOR SHEET FEEDING DEVICES Daniel Broido, Gockfosters, near Barnet, England Application May 18, 1942 Serial No. 443,541 In Great Britain August 15,. 1941 Claims.

This invention relates to machines through which paper and like sheets are passed, such machines being provided with feeding devices for feeding the paper or like sheets into the machine.

It has been found that however carefully the :teeding device is adjusted sheets will occasionally be fed into the machine in inaccurate alignment with parts of the machine which are to act on, or co -operate with, the sheets.

Further, in some machines of'the kind in question, for example the asserting machine disclosed in my prior U. S. A. Patent No. 2,319,108, printed sheets are to be fed into the machine; in such cases in order to be acted upon properly by the machine, not only must the sheets v be fed accurately into the machine, but the printed matter must also be accurately positioned on the sheet in order to obtain correct operation of the machine. Again, it is possible for the feeding device to pick up and forward to the machine more than one sheet.

Further the machine may miss a sheet, or a blank sheet may be fed through the machine.

All these possible inaccuracies may lead to faulty operation of the machine, particularly where, as in the apparatus disclosed in the above -mentioned prior specification, the machine includes a photo-electric analysing device for analysing marks on the sheets passing through the machine.

Sheets which have been incorrectly printed or fed in any one of the ways above described are referred to in the appended claims as in.- correct sheets, in contradistinction to other sheets termed in the appended claims "correct sheets.

The object of the invention is to provide means for ensuring that the operation of the machine is effected only by correct sheets.

The accompanying drawings illustrate, by way of example, one embodiment of the present invention incorporated in the asserting machine described in my aforesaid prior Patent No. 2,319,108.

In the drawings:

Figures 1 and 1a together represent a vertical longitudinal section through a machine fitted with a control device according to the invention;

Figure 2 is a vertical transverse section on line ."III of Figure 1;

Figure 3 is a plan view taken substantially on line III-HI of Figure 1;

Figure 4 is a partial side view of the machine;

Figure 5 shows a record intended for use with the control device according to the invention;

Figure 6 is a side view, similar to Figure 4, of a modified control device according to the invention;

Figure 7 is a partial section on line VIIVII of Figure 6; and

Figures 8 and 9 illustrate variations of control marks for use with the control device according to the invention.

For a full description of the construction and operation of the assorting machine reference is made to my prior patent above referred to. Fig ures 1, 2, 3 and 4 of the present applicationcorrespond to Figures 1, 2, 3 and 8 respectively, of said prior patent. The machine-is adapted to assort or segregate records, such as shown in Figure 5, which have certain information recorded by selectively blacking in the index areas 98 provided for this purpose, each index area having a particular significance.

The operation of the machine is, briefly, as

follows: The records l3 are stacked in a paper A container 5 (Figure 1), and are fed between a drum 2| containing a photocell 80, and a lamp 12. The feeding device is of a known kind in ,which the top sheet I3 is first separated by buckling it between the feed roller 14 and a stop bar I! (or the back plate 8), thereby withdrawing it from underneath spring-loaded fingers l6, whereupon the feed roller H reverses its movement and causes the paper sheet to pass over the top of the fingers l6 and between guides l1, 18 on to stops I! carried on paper aligning fingers 20 pivotally mounted ina flap of the drum 2|. The means for operating the feed roller H, as also the means for operating the pinions in to raise the paper container 6, are not shown in the drawings but are fully described in U. S. A. Patent specification No. 2,165,281. Drum 2| has a number of apertures 9| corresponding in number and arrangement to the index-points 98 which are normally closed by plugs 92. In order to segregate records having certain index-points blackened, the apertures 9| in the drum corresponding to these index-points are opened. During each rotation of drum 2|, these open apertures, if the record is fed correctly through the machine, are

aligned with the corresponding index-points, and if all these index-points contain black marks, no appreciable amount of light will penetrate to the photocell an, and the record will be guided underneath a sorting flap 69 into a bin 10 reserved for accepted" records. However, if a record is not marked in the required indu-points, some or all open apertures II will not be cancelled by black marks when in the analysing position, and consequently an amount light sufilcient to trip the photocell will penetrate into the interior of drum 2]. The photocell Bil when tripped actuates a magnet H0 (Figure 4) to close the sorting fiap 89, as shown in dotted lines in Figure 1, which guides the record 13 into another bin 1! reserved for wrong records.

It will be evident that in order to ensure proper selection of records, the index points on each record must be accurately aligned with the analysing apertures Si. However, as above mentioned, even a carefully adjusted paper iced may occasionally rfail to move a record exactly into analysing position; further, some records may be inaccurately printed, or may be damaged, or they may stick together. In each case, such incorrectly printed, fed, or damaged records (referred to commonly as incorrect records") will not be properly analysed by the machine.

According to the present invention a control device is arranged to prevent all such incorrect records from being analysed by the machine, and to separate them from "correct records.

In the embodiment of the invention shown in the drawings, the control device is actuated by a control mark 200, Figure 5, printed on each rec- -orci 12 between the leading edge and the indexpoints 82 in such a way that the control mark 200 cuts across the beam of light before the first row oi. index-points are aligned with the first row of analysing apertures 21. As shown in Figure 2, a lamp 2, additional to the lamp 12, is mounted, underneath the drum 2|, in a socket 202, secured to a bracket 20.! fixed to casing 18 oi the analysing lamp 12, so that both lamps 2H, 12 are sub stantially in the same plane. Secured to the bracket 20! is a casing 20 enclosing the lamp 2M and provided with an aperture 20! facing the drum 2i, the i'eed roller 21 0f the machine being recessed as at 2" to allow tree passage of light to an aperture 221 in the wall of the drum. For the purpose of illustration this control aperture 201 is shown in Figure 2 in the same plane as a row of analysing apertures II, but in practice it is actually positioned in front of the latter, viz: in a position in which it will be able to co-operate with the control mark 200 on records it before the analysing apertures ll come into operation. The size or control aperture 221 corresponds to the open area within the control mark 2", so that the beam or light, alter passing through aperture 2" and the said open area, illuminates an area on drum 2i approximately equal to the control aperture 221'. Thus, assuming the control mark is accurately centred relatively to the aperture 281, a beam or light having a crosssection equal to the area or the control mark will pass through the aperture 221. As shown in Pigure 2 slotted mask II (similar to mask 12 of the above mentioned prior specification) is preferably provided close to drum 2! in order to prevent stray light impinging on the drum.

A photocell 222 in casing 2 open at the bottom is arranged in the interior oi drum 2| in line with the beam 01' light generated by control lamp 2M: it is mounted in a socket 222 fixed to a bracket 2" secured to stationary shaft ll of drum 2|; wires 2 connect the control cell 2 to the amplifier device 28 (Figure 1). The impulses of control cell 2, after being amplified, areconvcyed to an electromagnet 2|! (Figure 4) through wires 2". Magnet! is mounted in a bracket 2 ll fixed to frame plate 2 by screws 216, a set screw 2|1 securing the magnet in position. An armature 2I8 pivoted as at 2|! in frame 2, and biased by a spring 220, is arranged to cooperate with magnet 2I2. Armature 218 serves as a latch coacting with a stud 221 on a bail 222, fixed to a shaft 223 journalled in frame plates 1, 2, a spring 224 tending to swing bail 222 clockwise as viewed in Figure 4. Shaft 223 carries a deflector fiap 225 formed of three like members fixedly mounted on the shaft in a slot 226 (Figures 3 and la) formed in paper guides 61, B8.

The armature H8 is normally locked in the position shown in Figure 4 by means to be described hereafter, and it is momentarily released from the locking means when the control mark 200 on a record it! is aligned with the control aperture 201. Ii the record or like sheet has been accurately fed into the machine the control mark 200 will be properly aligned with the control aperture 221, the full area of the aperture will be exposed to light passing through the blank area within the control mark, and the control cell 208 will be fully illuminated; the

amplified impulse of cell 208 will energise the magnet 2", which will hold its armature 2", thus latching stud 22! and ball 222. Thus, the flap 225 will remain in position shown in full lines in Figure 10, that is, below the channel formed by guides 01, BI, and allow therecord ii to pass either underneath or above the sorting fiap $2. which is controlled in accordance with the analysis of the index-points 88 as described in the above-mentioned prior specification. However, if ior any reason the record I! has not been properly fed, control mark 200 will partially or wholly obscure the control aperture 201, control cell 2" will not be sufilciently illuminated to energise magnet 212, and spring 220 will rock the armature Ill clockwise, as viewed in Figure 4, on to a stop 221, thus idelatching stud 22! on bail 222, which'wlll be rocked by its spring 224 on to a stop 22.. Consequently, shaft 223 will also rock clockwise, thus elevating flap 225 into position shown in dotted lines in Figure 1, so as to intercept the incorrect record 12 and to guide it into a bin 22! reserved for incorrect; records. It will be noted that, as the blank area within the control mark 200 is entirely enclosed by the black area, a maladjustment of the record in any direction will partially or wholly obscure the control aperture 201.

It a record has been correctly fed, but the index-points 22 have not been accurately printed on the record, it can be assumed that the control mark 2", too, has not been printed in the exact position it should occupy. Consequently, when the record is in the control position, control mark 22! will be somewhat out of alignment with control aperture 201 and obscure the latter; thus, fiap 2" will be operated as described, and the record eliminated. It may be pointed out that it the conbol mark 2" is entirely out 01' alignment with aperture 221, the cell 2" will operate as it there was a perfect alignment; thus, in the present embodiment the control mark must be sufiiciently large to cope with any inaccuracy of P per iced such as is likely to occur in practice.

In case of, double feed, the two records will obscure the control aperture due to the reduced transparency of two thicknesses of paper as compared with a single thickness, the magnet 2i! will not be energised and the control device'will opcrate the fiap 22! as described to deflect the two recordsintothebin 222. .Thus. itwillbeaocn that. the control devicewill be operated whenever there is an incorrect record, and in this manner the incorrect records are eliminated before they reach the sorting fiap 63 which, thus, controls the selection of only properly fed and properly printed records.

The control device above described must operate only when control mark 200 on a record is just passing through the controlling beam of light; this i ensured by the locking device above referred to and now to be described. A cam 230 (Figure 4) having a recess 23l is rigidly mounted on drum 2| so as to rotate therewith. Cam 230 co-operates with a roller 232 journalled in a lever 233 pivoted as at 234 and biased toward the cam by a spring 235. The opp site end of lever 233-carries a trigger 236 pivoted as at 231 and biased by a spring 236 on to a stop 239. Trigger 236 co-Operates with a stud 240 carried on the armature 218, and it will be seen that in the posi tion shown in Figure 4 the armature 2| 6 is locked by the trigger 236 abutting against stop 239.

Cam 230 is so set relatively to drum 2|, which of course rotates in synchronism with the paper feed, that its recess 21 is aligned with the roller 232 at the exact moment when control mark 200 on record I3 is, or rather ought to be, aligned with control aperture 201. When roller 232 drops into recess 23!, lever 233 swing anti-clockwise, and trigger 236 releases stud 240, so that armature 218 is free to swing out if permitted to do so by magnet 2 I 3. Immediately afterwards roller 232 is moved out or recess 23l, thus restoring lever 233 and trigger 236, which again locks stud 240 if armature 2 i8 has remained in the latching position. However, if the armature 2; ha been moved away from magnet 2l3, under the action of the spring 220, trigger 235 when being restored just misses the stud 240, and armature 216 will remain in the delatched position until restored by means new to be described, whereby stud Mt strikes trigger 236 and swings it out oi the way by stretching its sprin 235,

Flap 225 and armature M are restored after each operation by means similar to those described in my above mentioned prior specification 2,319,108 for restoring sorting flap 66 and arms ture I06 of sorting magnet H0. A rod I it is shifted to the right (as viewed in Figure 4) after each revolution of drum 25 by cam 52 and lever 324. Fixed to rod i2! is a bush 24l'having a finger 242 aligned with an extension 243 on armature 2l6. Slidably mounted on red MI is another bush 244 having a finger 245 aligned with bail 222 on shaft 223, a spring 246 normally pushing bush 244 on to a stop 221. When the rod I2! is pushed to the right, finger 245 engages bail 222 and rocks it until it abuts against a stop 248, thus restoring shaft 223 and flap 225, whereupon finger 242 restores armature 2 It. When rod l2l again moves to the left, fiap 225 remains in the lower position shown in dotted lines in Figure 4, ball 222- being latched by armature 218, and the latter being locked by trigger 235. a V

In many cases machines or the type affected by the present invention have not only to sort records but also to perform further operations, such as counting or totalizing. For instance, the sorting fiap 69 of the sorting machine described-in my aforesaid prior U. S. A. Patent specification No. 2,319,108 may be arranged to operate a counter for rejected records. It will be evident that should the paper Ieed miss a record, the flap" of a wrong record, thus giving a wrong total of rejected records.

This will also be the case if a blank sheet (that is a sheet not having a control mark) is fed through the machine, or ii a record is so badly fed that the control mark is completely out of alignment with the control aperture 201.

A modified form of control device may be provided according to a modification of the present invention to eliminate this possibility by rendering the analysing device operative only when a single properly printed record is properly aligned with the controlling beam of light. Thus, if there is no record in the control position, or if the record is incorrect or in the case of a blank, the analysing device is rendered inoperative.

In this modification, shown in Figures 6, 7, the control cell 208 is arranged to operate a magnet 250 in exactly the same manner as previously described with reference to magnet 2l3. magnet 250 is of solenoid type, its core 251 being linked as at 252 to a three-armed rocker 253 pivotally mounted as at 254 in frame plate 2. A downwardly extending arm of rocker 253 carries a stud 255 against which normally abuts a stud 256 secured to a bail 251 which, similarly to bail 222 of the first modification, is secured to shaft 223 carrying control flap 225, and is biased clockwise by spring 224. An upwardly extending arm of rocker 253 carries a stud 256 which is normally embraced by a bifurcated end 259 of a doublearmed lever 260 pivoted as at 26!, which is, similarly to lever 233 of the first modification, biased anti-clockwise by spring 235 and carries a roller 232 coacting with a cam 262. Cam 262, which has two recesses 263, 264, is rigidly mounted on drum 2!, similarly to cam 230 of the first modification. Recess 253 is so positioned on cam 262 as to be aligned with roller 232 just when the controi mart: 200 on a record i3 is aligned with control aperture 201 in drum 2|; at thismoment, roller 232 drops into recess 263, the bifurcated lever 260 swings anti clockwise and releases stud 253 of rcclrer253, which is then free to be operated by control cell 208 as will be presently described.

A second solenoid magnet 265 is secured to frame plate 2 opposite magnet 250, its core 265 being linked at 252 to rocker 253 similarly to core 251 of magnet 250. Wires 261 connect magnet 265 to a permanent source of current indicated as at 263. The magnets 250, 265 are arranged to pull in opposite directions, and are so adjusted that, when control mark 200 is properly aligned with control aperture 201, the resulting full illumination of control cell 208 energises magnet 250 to such an extent that its pull is equal to. the permanent pull of magnet 265. Consequently, in this case the rocker 253 will remain stationary, its stud 255 continuing to latch stud 256 on bail 251,so that the control flap 225 will remain in the lower position indicated in dotted lines in Figure 6, and the record will not be intercepted, as heretofore described. 3

In the case of double feed, or if the control mark 200 is not properly aligned with control aperture 201, the control cell 208 will receive a reduced amount of light, and consequently a reduced current impulse will be transmitted to magnet 250; thus, its pull will be less than that of permanent magnet 265, and consequently rocker will be operated in the same manner as in the case 253 will swing out clockwise as viewed in Figure 6, its stud 255 delatching stud 255 on bail 251; the latter will be elevated by its spring 224, thus causing the control flap 226 to move into the ele-- This I vated or open position indicated in dotted lines in Figure 1, and the record will be intercepted and guided into bin 229. Should it so happen that a portion of a record 13 containing the control mark 200 be torn off, or should the paper feed miss a record, no paper will be interposed between control aperture 201 and lamp 20! when recess 263 in earn 252 causes lever 260 to release rocker 253. Consequently, the control cell 208 will receive a greater amount of light than it would normally receive through a thickness of paper, and the impulse transmitted to magnet 250 will be correspondingly greater and will exceed that of permanent magnet 265. Consequently rocker 253 will swing out anti-clockwise as viewed, in Figure 6, thus delatching bail 257 to open control flap 225 as described.

Bail 25'. has an extension 263 carrying a lug 21B of insulating material, which is adapted to co-operate with a pair of contacts 2! l. The analysing magnet H is normally energised and is arranged to be deenergised by the analysing cell 80 to operate the sorting flap B9. The magnet llll has two windings, namely, the usual or primary winding connected by wires H8 to ampliiler device 88 and controlled by the analysing cell 80 in such a way that the circuit is broken by impulses from the cell, and a secondary winding connected by wires 2.12 to a permanent source of current indicated as at 213. The secondary winding 2H is'normally ineffective, as the contacts 21! are normally open, thus cutting off the supply of current 213. However, during every operation of bail 251 and control flap 225, the lug 210 closes contacts 2", thus establishing a circuit through secondary winding 212; consequently, the analysing magnet H0 remains energised regardless of any operation of the primary winding 1 l8 by the analysing cell 80, so that this energising of the secondary winding 212 amounts to cutting-out the analysing device whenever an incorrect record is fed through the machine. If the analysing magnet H0 were arranged to be energised (and not, as in the present case, to be deenergised) by the analysing cell 80 in order to operate the analysing device, the lug 210 would be arranged to break the circuit of the analysing 'magnet H6, thus rendering it ineflective with regard to incorrect records; in this case, secondary winding 212 and permanent source of current 213 could be dispensed with.

Movement of rocker 253 can be adjusted by set screws 2' in a bracket 215 secured to frame plate}. After each working cycle, rocker 253 and ball 251 are restored by members 242, 245 as already described with reference to armature 2|! and bail 222, respectively, of the previously described modification (if the rocker 253 has been previously swung clockwise asviewed in Figure 6) thus restoring the control flap 225. If the rocker 253 has been swung anticlockwise, it is restored by a finger 242 secured to the rod l2l, its upper end being in line with the lower end of core 25! of the magnet 250. The top part of finger 242 is sloped to form a cam surface which, when the finger is shifted to the right as viewed in Figure 6, pushes the core 25! upwards and so restores the rocker 253 into the normal position. Prior to this restoring operation, however, the bifurcated end III of lever must be moved out of the way of stud 258 on rocker 253. For this p p s the second recess 2 is arranged in the cam in such a position as to be alignedwith roller 23! on lever 2" Just prior to the restoring operation of rod l2l, thus causing lever 260 to clear rocker 253 as already described.

A already mentioned, a control mark of the kind shown in Figure 5 will not operate the control mechanism if it is completely out of alignment with control aperture 201; this will also be the case if a blank sheet without any control mark is fed into the machine. In order to meet this possibility, however remote, control marks of the kind shown in Figures 8 and 9 may be used. These marks difier from the mark shown in Figure 5, in that a small opaque area is inserted in the blank or transparent area within the control mark, this additional opaque area being of any suitable shape. For use with control marks of this kind, the magnets E50, 265 are so adjusted that their pull are equal when the control cell 208 receives light passing through the remaining transparent area within the control mark. It will be seen that if, at the time of control operation, a blank portion of a record be exposed to the controlling beam, an amount of light greater than the standard amount will reach the control cell; consequently, the pull of magnet 250 will exceed that of permanent magnet 265, thus operating the control flap 225 as described. Otherwise, the control operation is exactly the same as in the cas of the control mark illustrated in Figure 5.

The control device according to the present invention has been described with reference to light energy, but it will be evident that any other suitable form of radiant energy (for instance, infra-red rays) can be used, providing it is capable of being influenced by semi-transparent paper sheets. If another form of radiant energy were to be used, the light source 2M, the photocell 208, and the control marks 20!] would be replaced by devices generating, sensitive to, and impervious to, respectively, the particular form of radiant energy used.

This invention is not limited in its application to the assorting machine described in my above mentioned prior patent; it may be usefully applied to sorting, segregating, selecting, accounting, tabulating, interpolating, counting, typesetting, repetition printing and other machines using printed or otherwise marked sheets or records. whenever these machines require accurate feeding for proper operation.

What I claim is:

1. In a machine having a feeding device for paper and like sheets, means for segregating incorrect sheets from "correct" sheets, comprising a photoelectrical analysing device adapted to cooperate with a control mark on the sheets fed into the machine in order to produce standard impulses in the case of accurate feeding of the sheets, and non-standard impulses in the case of inaccurate feeding of the sheets, an electromagnetic device operatively associated with said analysing device and adapted to be actuated only by said non-standard impulses, mechanical holding means for rendering the electromagnetic device inoperative until such time as the control mark on a sheet shouldjin the case of accurate feeding, be in alignment with the analysing device, means for thereupon momentarily releasing said holding means, said holding means and said releasing means comprising a. cam rotating synchronously with said paper feeding device, means for operatively associating said cam with said magnetic device, and a deflector flap operated by said magnetic device when the latter is actuated to deflect the sheets responsible for producing the non-standard impulses so that they do not cooperate further with the machine.

2. In. a machine according to claim 1 a locking member adapted to be displaced by the non.. standard impulses received by the electromagnetic device to hold the machine inoperative for the remaining of the working cycle of the mach'ine.

3. A machine according to claim 1 wherein the electromagnetic device comprises a latching member adapted normally to latch the flap in an inoperative position, said latching member constituting an armature for the electromagnetic device which normally maintains the latching member in latching position, and further comprising aspring acting on said latching member and tending to move it into the unlatched position, and means for restoring the latching menuher, when it has been deiatched, into the iatching position before each fresh cycle of operation.

4-. A machine according to claim 1 wherein. the electromagnetic device comprises one magnet exerting a substantially constant force, a second magnet controlled by impulses received from the sensitive device and arranged to exert a force opposite in direction to that exerted. by the first magnet, and. an element movable from a normal position in either direction under the resultant action of said magnets, said element normally latching the deflector flap in an inoperative posttion and unlatching said deflector flap for operation when moved in either direction from the normal position.

5. A machine according to claim 1 wherein the electromagnetic device comprises one magnet exerting a substantially constant force, a second magnet controlled by impulses received from the sensitive device and arranged to exert a force opposite in direction to that exerted by the first magnet, a latching device normally latching said deflector flap in an inoperative position but mothable under the action of said magnets to delatch said deflector flap, and means for restoring said latching device, when it has been delatched, into the latching position before each fresh cycle of operation.

6. Amachine according to claim prising a drum the wall of which has an aperture and which is adapted to move between the source of radiant energy and the device sensitive thereto, and means for rotating said drum to bring said aperture into alignment with the source 01' radiant energy and the device sensitive thereto simultaneously with the control mark on a correct sheet, whereby the correct alignment or otherwise of said control marl: relatively to said aperture controls the operation of the deflector flap.

1 further com-- 7. Amachine according to claim 1 further comprising a photoelectric analysing device for analysing record cards and like sheets.

8. Amachine according to claim 1 further comprising a photoelectric analysing device for analysing record cards and like sheets, an electric switch controlling the operation of said photoelectric analysing device, and means for operating said switch to render said analysing device inoperative when the deflector nap is moved to deflect an incorrect record.

9. In a control device for use in machines through which paper and like relatively transparent sheets are passed, mechanism designed to prevent normal operation of the machine by incorrect sheets, a source of radiant energy, a device sensitive to said radiant energy, an opaque mask operatively disposed in the path of the radiant energy between said source of radiant energy and said sensitive device, said mask. having a transparent area arranged to co-operate in. a control position in the machine with a control marl; comprising a transparent area enclosed in an opaque area provided in a predetermined position on a sheet passing through the machine,

whereby the maximum amounts of radiant energy,

which can pass through the said two transparent areas are substantially equal in the case of correct" records and unequal in the case of incorrect records, and means operated by said sensitive device, when the amounts of radiant ener y passing through the two transparent areas are unequal, to operate saidmechanism.

10. In a control device for use in machines through which paper and like-sheets are passed, mechanism designed to prevent normal operation of the machine by incorrect sheets, a source of maximum amount of radiant energy which can pass through said inner portion is less than that which can pass through the transparent area insaid mask, and means, operated by said sensitive device, for operating said mechanism whenever the amount of radiant energy impin in on the said sensitive device differs from said maximum amount.

DANIEL BROIDO. 

